More precisely, it concerns the conditioning of radioactive or toxic waste stored in water, and especially radioactive waste comprising ion exchanger resins and/or acid compounds.
In nuclear installations, ion exchanger resins are particularly used to purify the contaminated water, especially the waste of these installations. After some time, these resins are subjected to degradation phenomena and consequently lose their effectiveness. Given the fact that, during their use these spent resins have immobilized a certain number of radioelements, it is therefore necessary to condition them in a suitable material so as to ensure that their radioactivity is properly retained.
Given the fact that waste consisting of acid-function materials is also found in nuclear installations, for example acid compounds, such as salts like lead iodide in the form of a powder or grains in a humid environment, it is therefore necessary to also carry out conditioning after use so as to ensure that the radioactivity immobilized on the materials is properly retained.
Amongst the methods currently developed to process this type of waste, there are known methods for conditioning in thermosetting resins, such as epoxy resins. These methods are detailed in the French patents FR-A-2 251 081, FR-A-2 361 724, FR-A-2 544 909 and FR-A-2 577 709.
In the first three French patents which apply in particular to the treatment of exchanger resins, provision has been made to either directly encapsulate the ion exchanger resins in the thermosetting resin (FR-A-2 251 081), or to subject the resins to a pretreatment so as to saturate their active centers by a basic compound and afterwards encapsulate them in the thermosetting resin (FR-A-2 361 724), or to use suitable aminated hardening agents with epoxy resins in order to directly embody an encapsulation so as to carry out this saturation at the time of hardening and to avoid pretreatment by a basic compound. In all these cases, the waste stored in the water is first of all dried before being incorporated in the thermosetting resin and hardening agent mixture so as not to encapsulate the water in which they have been transported and stored.
However, implementation of this preliminary stage involves certain drawbacks. In fact, at the time of final mixing of the dried waste with the resin and the hardening agent, it is difficult to stop air entering the mixture owing to the viscosity of the products used and the rise in temperature resulting from the exothermicity of the reactions. This presence of air constitutes a drawback, since firstly it reduces the density of the solid block and secondly it increases porosity to the detriment of the confinement power.
Therefore, it would be advisable to improve the methods previously described so as to prevent air from entering into the final product.